The present invention relates to a titanium oxide-containing substrate that has various functions such as deodorizing, stain resisting (stain proofing or stain releasing), and antibacterial functions because of the photo-catalytic action of titanium oxide, and a process for preparing the same.
Conventionally, it is known that titanium oxide has a photo-catalytic action, by which it decomposes organic matters. The mechanism of decomposing organic matters by this photo-catalytic action is as follows: When titanium oxide is irradiated with light such as visible or ultraviolet rays, charge separation occurs, and electrons and highly oxidizable electron holes are formed. The electron holes react with water vapor or oxygen in air to form reaction active species such as OH radicals or O2xe2x88x92, which decompose organic matters that are present around them instantly. At present, titanium oxygen is used for environmental clean-up of deodorizing, stain resisting, and antibacterial treatments etc. by utilizing its photo-catalytic action.
However, although adhesives have been used for attaching titanium oxide to materials such as metals, glass, wood, or the like, there has been a problem that the adhesives are deteriorated by the photo-catalytic action of titanium oxide, so that the attached titanium oxide is peeled off. Furthermore, when titanium oxide is attached to a substrate formed from resins, synthetic fibers, or the like, it may be attached by mixing it in the substrate during the formation of the substrate, instead of using adhesives as mentioned above. It is herein noted that light such as visible or ultraviolet rays is required for causing the photo-catalytic action of titanium oxide, and moreover, it is necessary that titanium oxide exists on the surface of the substrate so that it may contact with an organic matter that is to be decomposed. However, according to the above-mentioned mixing method, it is difficult to attach titanium oxide on the surface of the substrate, and a large amount of titanium oxide should be mixed in the substrate so that titanium oxide may exist on the surface of the substrate in an amount required to develop various functions such as antibacterial, deodorizing, and stain resisting functions effectively. As a result, this method may affect properties of the substrate, and also is disadvantageous in terms of cost performance. Furthermore, when the substrate is formed from organic matters such as synthetic fibers, resins, or the like, the portion at which titanium oxide is attached is deteriorated, so that the titanium oxide may be peeled off.
Thus, it is an object of the present invention to provide a titanium oxide-containing substrate in which various functions such as deodorizing, stain resisting, and antibacterial functions due to the photo-catalytic action of titanium oxide are displayed sufficiently, and a process for preparing the same, by developing an effective means for attaching titanium oxide to a surface of a substrate, in which peeling of titanium oxide is prevented.
In order to achieve the above object, the present invention provides a titanium oxide-containing substrate having a surface plated with an anatase type titanium oxide film, the film being adhered to the surface of the substrate without being burned.
Thus, when the substrate has a surface plated with titanium oxide, even if the substrate is formed from organic matters, the portion at which titanium oxide is attached is not deteriorated by the photo-catalytic action of titanium oxide.
Moreover, because the bonding strength of plating is large, titanium oxide is not peeled off. Furthermore, because a surface of the substrate is plated with titanium oxide, the photo-catalytic action of titanium oxide is displayed sufficiently, so that the substrate exhibits various functions such as excellent deodorizing, stain resisting, and antibacterial functions.
In the present invention, the surface of the substrate may be coated with titanium oxide completely, or may be coated partially. It is preferable that titanium oxide is attached to the surface of the substrate uniformly in a ratio of 1 to 10% (particularly a ratio of 2 to 5%) on an area basis.
In the titanium oxide-containing substrate of the present invention, it is preferable that the substrate is at least one selected from the group consisting of synthetic fibers, glass, metals, resins, and wood. Moreover, the substrate also may be formed from proteins, cellulose, or the like.
In the titanium oxide-containing substrate of the present invention, it is preferable that a noble metal is included in the titanium oxide film. This is because the photo-catalytic action of the titanium oxide is further accelerated by incorporating the noble metal, and also effects characteristic of the noble metal can be obtained. Furthermore, it is preferable that the noble metal is incorporated by plating as in the case of titanium oxide.
Furthermore, in the titanium oxide-containing substrate of the present invention, it is preferable that gold is included in the titanium oxide film, and a function of decomposing organic matters by oxidation is developed even in the absence of light.
Moreover, in the present invention, the titanium oxide and the noble metal in the substrate may be either ionic or non-ionic.
Next, the process for preparing the titanium oxide-containing substrate of the present invention comprises: adding a titanium fluoride in an aqueous solvent to prepare a solution; and bringing the solution into contact with a surface of a substrate while adding boric acid, malic add, and citric acid to the solution; whereby the surface of the substrate is plated with an anatase type titanium oxide film. It is preferable that the pH of the solution in which boric acid, malic acid, and citric acid are added is in the range of 3 to 5.
In the process for preparing the titanium oxide-containing substrate of the present invention, it is preferable that titanium tetrafluoride is used as the titanium fluoride because of its excellent reactivity.
In the process for preparing the titanium oxide-containing substrate of the present invention, it is preferable that at least one selected from the group consisting of synthetic fibers, glass, metals, resins, and wood is used as the substrate. Moreover, other than these materials, those materials as mentioned above also may be employed.
Because of the same reasons as mentioned above, in the process for preparing the titanium oxide-containing substrate of the present invention, it is preferable that a noble metal is incorporated in the titanium oxide film.
Moreover, in the present invention, the xe2x80x9csubstratexe2x80x9d includes substrates after being processed into products as well as substrates before being processed into products. Furthermore, it also includes substrates formed on a surface of other objects, such as coating films.
The titanium oxide-containing substrate of the present invention is prepared, for example, as follows. In the following, xe2x80x9c% owfxe2x80x9d represents percentage by weight to the weight of the substrate to be treated. For example, 5% owf of an additive in the case of treating 3 kg of substrate indicates 150 g of the additive.
First, a substrate to be treated is prepared. The materials as mentioned above mentioned may be employed as this substrate. Furthermore, the shape of the substrate is not particularly limited, and it may be in the form of, e.g. fiber, plate, rod, or the like.
On the other hand, a titanium fluoride is added to an aqueous solvent to prepare a treating solution. Usually, water is used as the aqueous solvent. Furthermore, other than the above-mentioned titanium tetrafluoride, titanium trifluoride or the like also can be used as the titanium fluoride. In this case, the ratio of the titanium fluoride is usually from 0.1 to 5% owf, preferably about 2.0% owf Moreover, by changing this ratio, the ratio of the titanium oxide introduced into the surface of the substrate can be adjusted.
Then, the treating solution is brought into contact with the surface of the substrate. When titanium oxide is introduced into a portion of the surface of the substrate, only that portion may come into contact with the solution. When titanium oxide is introduced into the entire surface of the substrate, the whole substrate may be immersed into the solution. Moreover, prior to this surface contacting treatment, it is preferable that the surface of the substrate is washed with water sufficiently.
Next, boric acid, malic acid, and citric acid are added to the treating solution. By adding these adds, an anatase type titanium oxide film is formed on the surface of the substrate. Moreover, although an anatase type titanium oxide film can be formed by adding only boric acid, by adding malic acid and citric acid as well, an anatase type titanium oxide film that is dense and has good adhesion is formed. The degree of adding the three types of acids is controlled so that the pH of the treating solution becomes in the range of 3 to 5.
The above treatment is usually carried out under conditions at a temperature of 20 to 50xc2x0 C. and for 30 to 60 minutes, preferably at about 50xc2x0 C. and for about 30 minutes.
When the surface of the substrate is plated with an anatase type titanium oxide film by such a process, the titanium oxide is not peeled off until the substrate is broken. Moreover, photo-catalytic reaction does not develop in a portion at which titanium oxide is attached to the substrate, but it develops at the interface between the titanium oxide exposed from the surface of the substrate and air, so that the strength of the attachment is not reduced by the photo-catalytic action of titanium oxide.
Thus, a titanium oxide-containing substrate is produced without using an adhesive or the like.
The ratio of the titanium oxide that is introduced onto the surface of the titanium oxide-containing substrate of the present invention is usually from 1 to 10%, preferably from 2 to 5% on an area basis. Furthermore, in the present invention, although the titanium oxide that is introduced onto the surface of the substrate is usually titanium dioxide, it also may be titanium monoxide or titanic trioxide. Furthermore, as a titanium dioxide, it is preferable to use an anatase-type that is excellent in photo-catalytic function. After being washed with water, the titanium oxide-containing substrate of the present invention can be processed into a desired product.
Furthermore, the method for introducing titanium oxide onto a surface of a substrate according to the present invention can be applied to a substrate that has been processed into a product. For example, it is possible that a garment is produced by processing a synthetic fiber, and the above-mentioned method of the present invention is applied to this garment. Furthermore, when a substrate that is formed from wood, metals, resins, or the like is coated with a paint, and the above-mentioned method of the present invention is applied thereto, the surface of the coating film is plated with titanium oxide.
As mentioned above, in the present invention, it is preferable that a noble metal is included in the titanium oxide film. In the following, combinations of titanium oxide and noble metals are described.
Titanium Oxide and Gold
By attaching gold as gold ions to a surface of a substrate, the reactivity of active oxygen generated by the photo-catalytic action of titanium oxide to organic matters can be increased. For example, when titanium oxide and gold are attached to a surface of a substrate in the ratio by weight of 1:0.001 of titanium oxide to gold, decomposition of contaminating organic matters such as tar of tobacco can be accelerated. Although the active oxygen generated by titanium oxide does not have selectivity in its reaction, by introducing gold ions, the active oxygen is allowed to react selectively with harmful substances contained in smoke of tobacco, which are partially ionized. Moreover, the ratio by weight of titanium oxide to gold on the surface of the substrate is usually from 100 to 10,000:1, preferably from 1000 to 2000:1.
Titanium Oxide and Silver
In theory, titanium oxide does not develop its photo-catalytic action without light. On the other hand, it is known that silver exhibits antibacterial and deodorizing actions under a condition without light and also exhibits almost no toxicity, so that it has been used traditionally as a material of antibacterial agents and deodorants. Thus, by attaching silver to a surface of a substrate in addition to titanium oxide, antibacterial and deodorizing properties are developed regardless to the presence or absence of light. Furthermore, because of the activity of silver, ozone can be produced using moisture and oxygen in the air, and thereby the photo-catalytic reaction of titanium oxide can be further accelerated. Moreover, the ratio by weight of titanium oxide to silver on the surface of the substrate is usually from 10 to 100:1, preferably from 50 to 60:1.
Titanium Oxide and Zirconium
Zirconium ion is a highly active ion having a coordination number of eight. By introducing zirconium ions onto a surface of a substrate along with titanium oxide, the photo-catalytic reaction of titanium oxide can be accelerated. Moreover, the ratio by weight of titanium oxide to zirconium on the surface of the substrate is usually from 10 to 20:1, preferably 10:1.
Other than the above-mentioned combinations, a combination such as that of titanium oxide, silica, and silver also may be employed. The common thing in all of these combinations of titanium oxide and noble metals is that the noble metals accelerate or stabilize the photo-catalytic action of titanium oxide.
The noble metals can be introduced onto the surface of the substrate in accordance with the method for introducing titanium oxide. That is, a compound of each noble metal is dissolved in water along with titanium fluoride. Examples of the compound of noble metal include chloroauric acid, silver nitrate, and zirconium acetate. Moreover, the ratio of the compound of a noble metal to be dissolved is adjusted so that the ratio of the noble metal on the surface of the substrate falls in the above-mentioned range. Moreover, in the same way as the above, by bringing this solution into contact with a surface of a substrate while adding boric acid, malic acid, and citric acid to the solution, titanium oxide and a noble metal can be deposited (plated) on the surface of the substrate. Moreover, it is presumed that a noble metal (particularly gold) is absorbed between the molecules of titanium oxide during the deposition.